In the recent year, from the viewpoint of high reliability that would not impair properties of toners even under the various circumstances, together with the advancement of miniaturization, speed-up, and high-quality image formation of electrophotographic apparatuses, improvements in low-temperature fusing ability and durability are earnestly in demand for the toner used in electrophotography.
On the other hand, in a toner which is a developer for electrophotography, use of polylactic acid which is a plant-derived raw material is studied for the purpose of reduction in environmental loads.
For example, it is disclosed that a toner for electrophotography characterized in that a resin containing a degradable polyester resin containing a poly α-hydroxycarboxylic acid and a polyester-based resin other than the above is used as a resin binder gives favorable deinking ability and degree of whiteness, has favorable wax dispersibility, fusing ability, pulverizability, hot offset resistance and storage property, and has excellent properties as a toner for electrophotography (see, Patent Publications 1 and 2).
In addition, from the viewpoint of energy conservation, i.e. reducing energy consumption in the fusing step, together with the advancement of miniaturization, speeding-up and high-quality image formation of the electrophotographic apparatus, an improvement in low-temperature fusing ability of the toner is earnestly in demand. In order to meet this demand, a toner in which a resin binder containing a crystalline resin and an amorphous resin is used is proposed. However, while a toner in which a crystalline resin and an amorphous resin are used has improved low-temperature fusing ability, the toner is likely to have a lowered toner strength. As a result, if a toner is applied with a larger mechanical or thermal stress to meet the demands of the speeding-up and miniaturization, a disadvantage concerning the lowering of gloss or durability is generated.
In order to overcome such a disadvantage, for example, it is proposed that a toner having excellent low-temperature fusing ability, and also having favorable pulverizability and storage property can be produced according to a method for producing a toner including the steps of melt-kneading raw materials containing two or more kinds of polyesters, a heat-treating step, a pulverizing step, and a classifying step, wherein the two or more kinds of the polyesters contain at least one kind of an amorphous polyester, and wherein the heat-treating step is carried out at temperatures and time that satisfy a particular relationship (see, Patent Publication 3).
In addition, it is disclosed a toner containing a resin binder comprising a crystalline resin and an amorphous resin, and a colorant, wherein the crystalline resin contains a composite resin containing a polycondensation resin component obtained by polycondensing an alcohol component containing an aliphatic diol having from 2 to 10 carbon atoms, and a carboxylic acid component containing an aromatic dicarboxylic acid compound, and a styrenic resin component, and wherein the amorphous resin contains a polyester obtained from an alcohol component containing an aliphatic diol in an amount of 60% by mol or more, and a carboxylic acid component, the toner having excellent low-temperature fusing ability and storage stability, suppressed unevenness in optical density, shorter time period for a heat-treating step, and excellent productivity (see, Patent Publication 4).
In addition, from the viewpoint of high reliability that would not impair properties of toners even under the various circumstances, together with the advancement of miniaturization, speed-up, and high-quality image formation of electrophotographic apparatuses, improvements in durability of the toner and developability under high-temperature, high-humidity environmental conditions are earnestly in demand.
In order to meet this demand, for example, it is disclosed that a positively chargeable toner comprising toner matrix particles containing at least a colorant and a resin binder containing a polyester, and an external additive which is externally added to the toner matrix particles, wherein the positively chargeable toner contains    the toner matrix particles,    silica A having a BET specific surface area of from 50 to 200 m2/g which is surface-treated with an external additive a fluorine-based silane coupling agent, and    silica B having a BET specific surface area of from 50 to 200 m2/g which is surface-treated with an amino-modified silicone,    wherein the positively chargeable toner gives a wide transferable region even under high-temperature, high-humidity conditions is provided (see, Patent Publication 5).
In addition, it is disclosed that a toner for a nonmagnetic monocomponent development used in a developer apparatus holding a toner carrier in a noncontact manner with an electrostatic latent image carrier containing a resin binder, a colorant and an external additive, wherein the external additive contains (a) a hydrophobic rutile type titanium oxide having an average particle size of primary particles of from 5 to 30 nm which is hydrophobically treated with a silane coupling agent, (b) a hydrophobic silica having an average particle size of primary particles of from 6 to 14 nm which is hydrophobically treated with hexamethyldisilazane, and (c) a hydrophobic silica having an average particle size of primary particles of from 20 to 100 nm which is hydrophobically treated with a silicone oil, the toner for nonmagnetic monocomponent development having favorable transferability even under the high-temperature, high-humidity environmental conditions is provided (see, Patent Publication 6).
A polyester has excellent fusing ability and durability as a resin binder for toner, but has stronger negative chargeability as compared to a styrene-acrylic resin or the like, so that improvement of chargeability is needed in a case where a polyester is used as a resin binder for a positively chargeable toner. In view of the above, a technique of adding a charge control resin (CCR) having favorable positive chargeability is known as a means to improve positive chargeability of a polyester.
For example, it is disclosed a positively chargeable toner containing a resin binder and a charge control resin in which the resin binder contains two kinds of polyesters of which storage moduli are in a specified relationship, and the charge control resin contains a styrene-acrylic copolymer having a specified storage moduli, the positively chargeable toner providing favorable chargeability, and having excellent inhibition in the generation of background fog and excellent solid image quality (see, Patent Publication 7).
In addition, from the viewpoint of high reliability, together with the advancement of miniaturization, speed-up, and high-quality image formation of electrophotographic apparatuses, improvements in developability and flowability of the toner are earnestly in demand.
In order to meet this demand, chargeability and flowability are improved by treating the surface of toner matrix particle with an external additive such as fine inorganic particles, but it is known that when detachment of the external additive is occurred upon use of the toner, damages is generated on a photoconductor by detached external additive, and which in turn causes image defects. Therefore, a method for firmly immobilizing an external additive on the toner matrix particles in a proper amount is considered.
For example, a method for producing a toner including the steps of pulverizing a toner composition containing at least a resin binder and a colorant in the presence of fine inorganic particles having an average primary particle size of from 6 to 20 nm to provide toner matrix particles having a volume-median particle size of from 3 to 8 μm, and externally adding a silica having average primary particle size of from 25 to 60 nm to the toner matrix particle obtained (see, Patent Publication 8).
Patent Publication 1: Japanese Patent Laid-Open No. 2003-323002
Patent Publication 2: Japanese Patent Laid-Open No. 2002-55491
Patent Publication 3: Japanese Patent Laid-Open No. 2005-308995
Patent Publication 4: Japanese Patent Laid-Open No. 2012-8529
Patent Publication 5: Japanese Patent Laid-Open No. 2010-122306
Patent Publication 6: Japanese Patent Laid-Open No. 2004-258265
Patent Publication 7: Japanese Patent Laid-Open No. 2010-8579
Patent Publication 8: Japanese Patent Laid-Open No. 2007-328224